Abstract
The present work has investigated the diverse interactions of selected methylenedioxyphenyl compounds with hepatic components, both in vivo and in vitro. Many methylenedioxyphenyl compounds were found to be activated via the hepatic monooxygenase system, resulting in the formation of "active metabolites" capable of binding in a 1:1 ratio with the haem of cytochrome P-450. These methylenedioxyphenyl metabolite-cytochrome P-450 complexes were found to be very stable and could be formed both in vivo and in vitro. However, safrole or isosafrole metabolite-cytochrome P-450 complexes, generated in vivo, were found to be dissociated with relative ease in the presence of certain alternative Type I substrates of the mixed function oxygenase system. This time-dependent dissociation of the complexes was observed after their formation in vivo, but not in vitro. Safrole and isosafrole appeared to induce the formation of a novel haemoprotein of the cytochrome P-448 type. The spectral properties of the safrole- or isosafrole-induced haemoproteins were found to be similar to but not identical with those of cytochrome P-448. Isosafrole-related material was found to become bound to other hepatic cellular components in an apparently irreversible manner. Results obtained using a novel approach, utilizing isolated hepatocytes, were compared with those found in vivo and in vitro using microsomes. The data obtained indicated that the use of the isolated hepatocyte system is more reliable than the usual in vitro microsomal screen for covalent binding, which has many inherent pitfalls.